The present invention relates to a method for ultrasound measurement and to a device for ultrasound measurement as disclosed herein.
In particular, the present invention relates to the ultrasound measurement of the blood flow in the human or animal body through a dynamic or irregular orifice, for example an insufficient or stenosed heart valve, a constricted vein or artery or similar. It is desirable, for example, to determine the cross-sectional surface area of flow, hereinafter shortened to (effective) opening surface area, the volumetric flow rate and/or the flow volume in a diseased heart valve, in particular the return flow through a diseased heart valve, in order thereby to be able to determine the severity of a valve defect and, if appropriate, perform a heart valve operation with optimum results.
WO 00/51495 A1, which forms the starting point of the present invention, discloses an ultrasound measurement method in which pulsed ultrasound signals are emitted and the backscattered ultrasound signals are evaluated on the basis of the Doppler technique.
For example, in the case of an insufficient heart valve, in order to determine the opening surface area, the volumetric flow rate, the flow volume and/or a value proportional thereto (hereinafter also shortened to measurement values) of the blood return flow, the measurement area of a reference beam must lie within the vena contracta (beam constriction) in the return flow of the blood through the heart valve, and the measurement area of a measurement beam must completely cover the vena contracta of the return flow through the insufficient heart valve. The positioning of the measurement areas has hitherto only been possible manually, and it requires great manual dexterity and considerable experience on the part of the operator. Moreover, a problem of the known method is that the orifice of an insufficient heart valve can be several centimetres at its maximum extent and for this reason the orifice can no longer be completely covered by the measurement area of a conventional measurement beam.
U.S. Pat. No. 6,464,642 B1 discloses a two-dimensional, so-called multi-array transducer for ultrasonic diagnostic in general, wherein a three-dimensional region of interest, e.g. the heart of a patient, can be displayed and Doppler signals evaluated.
In the present invention, a spatial area/volume is sonified, i.e. exposed to ultrasound, by a transmit beam. The backscatter of different sample volumes of this sonified volume is detected and evaluated, wherein the sample volumes are located at least essentially in a common plane and have different cross sections transversal to beam direction, but at least essentially the same extension in beam direction. In the present invention, the term “measurement area” designates the sample volume with the respective cross section transversal to beam direction. The backscattered ultrasound waves are called “measurement beam” and “reference beam”, wherein the measurement beam has a greater measurement area than the reference beam. Preferably, the measurement area of the reference beam lies within the measurement area of the measurement beam. Thus, the terms “measurement beam” and “reference beam” designate in particular Doppler signals backscattered from the respective measurement area.
The object of the present invention is to provide a method and a device for ultrasound measurement of at least one of the opening surface area of a dynamic or irregular orifice through which a fluid flows, in particular blood, of the volumetric flow rate, and of flow volume through the orifice, permitting simple and preferably automated operation and/or an accurate measurement, in particular on a relatively large or irregularly shaped or dynamic orifice.
The above object is achieved by a method according to claim 1 or 13 or a device according to claim 21. Advantageous embodiments are subject of the subclaims.
According to one aspect of the present invention, the measurement area of the measurement beam, particularly within the heart, is moved three-dimensionally beforehand in a search mode, in particular by means of a suitably controlled matrix array transducer, while Doppler signals are continuously detected and are evaluated in respect of the occurrence of a Doppler spectrum characteristic of a vena contracta. For example, the measurement area is moved in a meandering configuration and in different planes in succession, in order to locate a spatial region in which there is a vena contracta of the fluid flowing through an orifice.
This greatly facilitates the practical application of the measurement method and the operation of a measurement device. In particular, automated detection of a vena contracta is possible without the operator requiring great experience or manual dexterity.
According to a further aspect of the present invention, and one which can also be realized independently, several measurement beams with offset spatial, partially overlapping measurement areas covering the orifice completely, and/or several reference beams with offset spatial measurement areas are evaluated for determination of the measurement values. This leads to several advantages.                The detection and evaluation of several offset measurement areas (these can optionally be the measurement areas of several measurement beams and/or of several reference beams) permit fine adjustment and, if appropriate, correction of motion or location during the measurement, so that it is possible to achieve a reliable complete coverage of the orifice by the measurement beams and/or a reliable positioning of a measurement area of a reference beam in the inside of the vena contracta of the fluid flowing through the orifice.        The mutually overlapping measurement areas of the measurement beams permit a reliable coverage of larger orifices too, so that improved and more accurate determination of the measurement values is made possible.        
In particular, it is proposed to use what is called a matrix array transducer to generate preferably only one transmit beam to sonify a broad volume and to detect, preferably simultaneously if possible or sequentially, the measurement beams of different broad measurement areas and preferably the reference beams of different narrow measurement areas. This permits a simple, versatile structure, in which the directions of the beams and the depth range evaluated, and consequently the position of the measurement areas, can be controlled, in particular moved and adapted, electronically.